The blue-sensitive cones of the macaque retina are selectively labelled by tissue-reactive dyes injected into the vitreous humor. We have examined the mechanisms of staining of these cones, their retinal distribution at different retinal eccentricities, the age-dependence and sex-dependence of this distribution, and we have analyzed the point-pattern spatial distribution of these cones. A number of different dyes have been tested, using both fluorescent and non-fluorescent dyes and both electron-dense and electron-lucent dyes. These studies and those of stained postreceptoral retinal cells provide information on the probable retinol circuitry of the blue-sensitive cone pathway of primate retina.